Surface weirs have long had widespread use as a means of controlling or measuring liquid flow rates. They are used in devices to skim liquid surfaces of unwanted materials and also in apparatus for separation of liquids having different densities. Chemical manufacturing processes, water treatment process, waste treatment processes and water pollution cleanup operations all use separating, flow regulating or skimming devices.
There is a variety of skimming devices in the prior art. One such skimmer is a weir skimmer, which typically comprises a barrier wall of adjustable height which allows oil floating on water to flow over the wall and into a collection trough while excluding water. Recovered oil is then continuously pumped from the collection trough to a storage or transport means. Weir skimmers operate well in calm water with large or contained spills which produce a relatively thick oil layer.
Disc skimmers ordinarily include a plurality of discs spaced apart coaxially along a rotating shaft which may be supported by floats to position the lower portion of the discs in the water. Oil contacts and adheres to the rotating discs and is removed by blades or wipers which direct the collected oil into a sump or other collection means.
Drum skimmers have also been used for removal of oil and other hydrocarbons from water surfaces. A drum skimmer consists of one or more large rollers, or drums, which rotate partly submerged in water. Oil attaches to the drum surface as the drum rotates through the oil-water interface. The attached oil is then removed by squeezing or scraping the oil from the drum surface.
Most of the weir devices in use as separating, regulating or skimming apparatus are somewhat limited in operation and applications. One such device is disclosed in U.S. Pat. No. 4,405,458 to McHugh, Jr. which can be mounted in a fixed installation, such as a connection to a standpipe or as a floating unit. The unit utilizes a float supported weir that is unattached to the apparatus, except for contact with an adjustable retainer, which sets the weir elevation and flow rate.
The pivoting weir is mounted within a close fitting guide collar which guides weir movement and provides a practical or liquid seal between these members. The liquid seal provides a lubricating film to insure free vertical movement. The unit responds to flow interruptions caused by disturbances or variations in the flow rate of the piping system connected to the unit. Flow rate fluctuations result in the lowering of the inside liquid level and a corresponding lowering of the weir edge.
U.S. Pat. No. 5,498,348 to Plink et al. discloses a mobile floating surface skimmer comprising a vessel having an inlet through which liquid from the surface of the body of liquid can flow into the vessel together with the debris and/or contaminants. An outlet is connected to a pump for removing liquid, together with the debris and/or contaminants from the vessel. A valve controls the flow of liquid into the vessel in response to the level of the liquid to maintain the inlet near the surface of body of the liquid wherein the valve is provided with a delayed response to cause the skimmer to oscillate vertically in the body of liquid so the debris is prevented from becoming lodged at the inlet. German patent DE 19512279 A1 to Becker discloses a device which is constructed such that the device rotates about an axis of rotation, however, the discharge means is connected rigidly to the collecting container. The discharge means is a hose which significantly influences the position of the container itself, relative to the top floating layer that is to be removed. Since the force exercised on the collecting container by the discharge hose is not only dependent on the weight of the hose, but also on the contents of the hose, the operation of the device is problematic in many applications. In addition, the German patent device functions discontinuously, in that it rocks back and forth, filling up with fluid in the forward position and discharging at the backward position. Further, this device can only be used in conjunction with floating elements, while the present invention can be used without the use of floating elements, that is, the discharge pipe can be mounted into the side of a tank containing the liquid media. The device described in the German patent can not be used in this manner.
None of the above prior art devices are as effective in skimming off thin top layers as the instant invention or they are more complex devices which are more expensive to manufacture and to maintain. More importantly, none of the above prior art devices are structured such that the discharge or suction line acts as an axis about which the collecting container rotates and self-adjust.
U.S. Pat. No. 6,287,460 discloses an improved skimmer or collecting container adapted to rotate over or about an effluent pipe. In operation, the collecting container will swivel back and forth about the axis through its asymmetrical tilting self-adjustment evolutions. The direction, and the angle of the swiveling movement results from the difference between the incoming flow into the vessel and the flow out through the effluent pipe. The construction provides a more or less self-adjusting system which is sensitive to limited flow and liquid level variations. However, the known skimmer also has multiple drawbacks. A major drawback of the known skimmer is that it has been found that there is always a certain degree of friction between the collecting container and the pipe, as a result of which the capacity of self-adjustment of the collecting container is merely present in cases where the driving force applying on the collecting container, required for making the container rotate in case of liquid level differentials, exceeds the frictional force applying between the collecting container and the pipe. In particular in an extreme substantially horizontal or lying position of the collecting container, it frequently occurs that the frictional momentum exceeds the driving moment, as a result of which the self-adjusting capacity is no longer present. In this latter case the collecting container will not tilt on its own power in case of increasing liquid level, but an external (manual) force is required to tilt the collecting container such, that the driving force will exceed the frictional force again, and hence to recover the self-adjusting capacity of the collecting container.
It is an object of the invention to provide an apparatus for continuously skimming off a top layer of a body of liquid having an improved self-adjusting capacity.